Decouple CAS process management from integration tests

This PR contains an another approach to getting Aker's test suite running in ActiveSupport 4.0 (and better future-proofing it).  My previous approach was https://github.com/NUBIC/aker/pull/30; it should be ignored.

This approach uses a pair of URL generation programs to set ports for all test-related services.  These generated URLs are paired with tasks to start a CAS callback and server manager.  Finally, the CI script has been changed to download, start, and stop CAS servers.